Homework Help:
Work Energy Theorem of a sled

1. The problem statement, all variables and given/known data
A sled with mass 8.00 kg moves in a straight line on a frictionless horizontal surface. At one point in its path, its speed is 4.00 m/s. after it has traveled 2.5m beyond this point its speed is 6.00 m/s. Use the work energy relation to find the force acting on the sled, assuming that this force is constant and that it acts in the direction of the sleds motion.

2. Relevant equations
W = ∆K

3. The attempt at a solution

The only thing i can think of (which isn't the work energy theorem) is Work = 1/2 MVf2-1/2MVi2

8.00 kg
moves in a straight line on a ... horizontal surface
At one point ... its speed is 4.00 m/s
2.5m beyond this point its speed is 6.00 m/s
find the force acting on the sled
assuming ... this force is constant and that it acts in the direction of the sleds motion

The value of theta has nothing to do with a straight line, it has to do with the angle between the directions of the force and direction traveled. theta is not 180. If theta were 180, then the force would be in the opposite direction from the motion, and so the object would slow down.